Intrinsic alignments of galaxies in the EAGLE and cosmo-OWLS simulations

Abstract

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Spherical cows in dark matter indirect detection

“…Our results found in projection are consistent with previous 3D analyses [55,[66][67][68][69][70][71][72][73][74][75][76][77]] (Ref. [54] shows a 2D projected misalignment angle of order 10 • ).…”

Intrinsic alignment of redMaPPer clusters: cluster shape–matter density correlation

“…However, haloes become rounder at large scales; the average ellipticity of redMaPPer clusters is ∼0.12 (see Table 1), a factor of ∼2 smaller than what is typically measured for the BCGs (Velliscig et al 2015;Huang et al 2016). This causes a similar reduction of the IA amplitude.…”

“…Velliscig et al (2015) measured the IA signal in the EAGLE simulations (Schaye et al 2015) and found that, when all star particles in each halo were used to estimate the shapes of galaxies, the IA signal of a LRG-like sample was overpredicted; however, by only using star particles inside a radius that contained half the stellar mass of the halo, the observations could roughly be matched. Tenneti et al (2015) measured the IA signal of a LRG-like sample in the MassiveBlack-II simulations and reported good agreement with observations for SDSS LRGs; however, they used a reduced inertia tensor to define the galaxy ellipticities, downweighting particles further away from the centre, effectively similar to what was done in Velliscig et al (2015). It is not yet clear how the shapes of galaxies in hydrodynamical simulations compare to the shapes of LRGs that are measured in the data.…”

“…Allgood et al 2006;Despali et al 2016) and their orientations change as well. For example, the mean misalignment angle between the dark matter distribution at the halo's centre and at the virial radius is ∼20 degrees for LRG-sized haloes in the dark-matter-only simulations of Despali et al (2016), while Wang et al (2014) and Velliscig et al (2015) report a mean 3-D misalignment angle between central galaxies and their haloes within the virial radius of ∼35 degrees using hydrodynamical simulations; the misalignment angle decreases for more massive haloes but does not become zero. These values are in line with the results from Huang et al (2016), who found mean misalignment angles between the position angle of redMaPPer BCGs and their satellite distributions of 32-35 degrees, depending on which shape measurement technique was employed.…”

“…Mandelbaum et al 2006;Okumura et al 2009;Hirata et al ⋆ vuitert@ucl.ac.uk 2007; Joachimi et al 2011;Li et al 2013;Singh et al 2015), in N -body simulations (e.g. Croft & Metzler 2000;Hopkins et al 2005) and in hydrodynamical simulations (Codis et al 2015;Velliscig et al 2015;Chisari et al 2015Chisari et al , 2016Tenneti et al 2016;Hilbert et al 2016). The picture that is emerging is that massive, red galaxies are pointing towards matter overdensities, which can be reasonably well described by the tidal alignment model (Catelan et al 2001;Hirata & Seljak 2004;Bridle & King 2007;Blazek et al 2011Blazek et al , 2015 at large scales.…”